Problem
Number the digits of n from the left, starting at 1. Raise each digit to the power of its position and add the results. For 352 that is 3¹ + 5² + 2³. A zero digit adds 0.
Implement digit_power_sum(n).
Input
n: A positive integer.
Output
Return the sum of the powered digits.
Constraints
1 ≤ n ≤ 1,000,000,000
Examples
Example 1
Input:
n = 352
Expected output:
expected = 36Input:
long long n = 352;
Expected output:
long long expected = 36;Input:
long n = 352;
Expected output:
long expected = 36;Explanation
3¹ + 5² + 2³ = 3 + 25 + 8 = 36.
Example 2
Input:
n = 89
Expected output:
expected = 89Input:
long long n = 89;
Expected output:
long long expected = 89;Input:
long n = 89;
Expected output:
long expected = 89;Explanation
8¹ + 9² = 8 + 81 = 89, the number itself.
How to approach it
Try on your own first, then open one hint at a time.
Hint 1
Scan the number digit by digit from left to right and keep track of each digit’s position.
Hint 2
Convert the number to a string or otherwise know the left-to-right index before combining each digit with its position.
Hint 3
Remember that a zero digit contributes nothing, but its position still matters for the exponent count.
Expected complexity
O(d) time, O(1) extra space